1. Field of the Invention
The present invention relates generally to multi-cavity injection molding and more particularly, to a method for controlling temperatures in hot runners of a multi-cavity injection mold, a warning method for a multi-cavity injection mold, and a control system based on those methods.
2. Description of the Related Art
The industries of semiconductor, optoelectronics, and ICT (information and communication technology) develop so fast that the market demand for varied specifications of consumer electronics and optoelectronics, which are light, thin, high-precision, and exquisite, is increasing. Therefore, domestic and foreign injection molding factories think highly of multi-cavity injection molding which has the advantages of mass production within a short time and resultant cost savings. However, it is subject to the defects of short shot, warpage, and different weights of the products, which result from the filling of the multi-cavity injection mold is unbalanced, which means that the volumetric fillings of individual cavities of the multi-cavity injection mold are not uniform, so that the production has low yield rate and needs long time for development.
To resolve the above-mentioned problems, a conventional method for controlling temperatures in hot runners of a multi-cavity injection mold is first positioning a temperature sensor at the end of the filling path of each cavity to send a temperature signal to a temperature controller, and then adjusting the temperatures in the hot runners by the temperature controllers so as to balance the volumetric filling of the cavities. Furthermore, a foreign-developed controlling method is defining a standard filling time as the average of the maximum and minimum filling time of the cavities which are spent on filling up the cavities respectively, and adjusting the temperatures in the hot runners after each injection cycle to make the filling time of the cavities of the next cycle closer to the standard filling time of the present cycle. As a result, the aforesaid method can balance the volumetric filling of the cavities after several injection cycles.
However, in aforesaid method, before the volumetric filling of the cavities is balanced, a new average was worked out after every injection cycle, which means that the standard filling time is changed constantly and susceptible to fluctuations of external environment. Besides, products made in the balanced condition may not meet the quality requirements, so the process parameters should be further adjusted. As a result, the product development of multi-cavity injection molding based on the conventional method not only requires a very long time but fails to work out satisfactory products.